The nervous system consists of the central nervous system (the brain and spinal cord), the peripheral nervous system (the sensory and motor neurons), and the autonomic nervous system

. All nervous systems in all animal species have four basic types of functional cells:

Sensory neurons

Motor neurons

Interneurons

Computation neurons

The nervous system has many types of sensory neurons. Nerve endings on one end of each neuron are encased in a special structure to sense a specific stimulus

Chemoreceptor's sense chemicals.). Taste buds have chemoreceptor's to detect chemicals dissolved in liquids. Chemoreceptor's in the brain also monitor the concentration of carbon dioxide in the blood and cerebrospinal fluid to help control your rate of breathing.

Mechanoreceptors sense touch, pressure and distortion (stretch). Stretch receptors in your muscle tendons are the first link in the knee-jerk reflex.

Photoreceptors, which sense light, are found in the retinas of your eyes.

Thermo receptors are free nerve endings that sense temperature, but we're not sure exactly how they do this. Changes in temperature could affect the movements of ions across the cell membrane and influence action potentials in that way.

Nociceptors are free nerve endings that sense pain. They respond to a variety of stimuli (heat, pressure, chemicals) and sense tissue damage.

Auditory receptors in the i006Ezner ear sense vibrations from sound waves.

DORSAL ROOT GANGLION

A motor neuron is a type of cell in the nervous system that directly or indirectly controls the contraction or relaxation of muscles,

Somatic motorneurons are directly involved in the contraction of skeletal muscles and are typically involved in locomotion.

-Special visceral motorneurons are involved in the motion of gills in fish and the motion of neck and facial muscles in vertebrates.

-General visceral motorneurons are directly involved in the contractions of the heart, the muscles of the arteries, and other viscera that are not consciously controlled.

Spinal cord ventral horn

inteneurons a neuron, or nerve cell, located entirely within the central nervous system . The central nervous system (CNS) consists of nerve cells within the brain and spinal cord

An interneuron acts as a “middle-man” between afferent,neurons, which receive signals from the peripheral nervous system, and efferent neurons, which transmit signals from the brain. It also connects to other interneurons, allowing them to communicate with one another.

CNS interneurons are typically inhibitory, and use the neurotransmitter GABA or glycine. However, excitatory interneuronsusing glutamate also exist, as do interneuronsreleasing neuromodulators like acetylcholine.

The vast majority of neurons in vertebrates are computation neurons. Computation neurons extract and process information coming in from the senses, compare that information to what’s in memory, and use the information to plan and execute behavior

Unipolar cells have one primary process that give rise to several branches. One of these is the axon and the rest serve as dendritic receiving structures. Unipolar cells have no dendrites arising directly from the cell's soma. These cells occur in certain ganglia of the autonomic nervous system of vertebrates

Bipolar cells have two processes emerging from the cell soma: a peripheral process or dendrite, the axon, which carries information toward the brain. These cells have mainly sensory functions: retina, olfactory epithelium and sensory cells of the spinal ganglia

Multipolar neurons have a single axon and one or more dendritic branches emerging from all parts of the cell body. Multipolar cells vary in the number and length of their dendrites and the length of their axons. The number and extent of dendritic processes depend on the number of synaptic contacts that other neurons make onto it.

People with AD gradually suffer memory loss and a decline in thinking abilitiesThese losses in cognitive function are accompanied by changes in the brain, including the build-up of amyloid plaques and tau-containing neurofibrillary tangles, which result in the death of brain cells and the breakdown of the connections between them.

Amyloid plaques and neurofibrillary tangles are the primary hallmarks of Alzheimer's disease. Plaques are dense deposits of protein and cellular material outside and around the brain's nerve cells. Tangles are twisted fibers that build up inside the nerve cells. Scientists have known about plaques and tangles since 1906, when a German physician, Dr. Alois Alzheimer, first identified them in the brain of woman who had died after suffering paranoid delusions and psychosis. Intensive research efforts of the last two decades have revealed much about their composition, how they form, and their possible roles in the development of Alzheimer's disease. The deposition of amyloid in the form of plaques is thought by many scientists to trigger the cascade of events leading to Alzheimer's pathology. The best evidence that amyloid causes the disease comes from the genetic studies in which mutations of APP, PS1, PS2 and APOE e4 (the genes so far identified as causing some cases of Alzheimer's) all facilitate amyloid accumulation

Are older. However, developing AD is not a part of normal aging. Have a close blood relative, such as a brother, sister, or parent with AD. Have certain genes linked to AD, such as APOE epsilon4 allele The following may also increase your risk, although this is not well

proven: Being female Having high blood pressure for a long time History of head trauma There are two types of AD: Early onset AD: Symptoms appear before age 60. This type is much less

common than late onset. However, it tends to get worse quickly. Early onset disease can run in families. Several genes have been identified.

Late onset AD: This is the most common type. It occurs in people age 60 and older. It may run in some families, but the role of genes is less clear.

The cause of AD is not clear. Your genes and environmental factors seem to play a role. Aluminum, lead, and mercury in the brain is no longer believed to be a cause of AD.

The early symptoms of AD can include: Difficulty performing tasks that take some

thought, but used to come easily, such as balancing a checkbook, playing complex games (such as bridge), and learning new information or routines

Getting lost on familiar routes Language problems, such as trouble finding the

name of familiar objects Losing interest in things previously enjoyed, flat

mood Misplacing items Personality changes and loss of social skills

As the AD becomes worse, symptoms are more obvious and interfere with your ability to take care of yourself. Symptoms can include:

Change in sleep patterns, often waking up at night Delusions, depression Difficulty doing basic tasks, such as preparing meals, choosing

proper clothing, and driving Difficulty reading or writing Forgetting events in your own life history, losing awareness of who

you are Hallucinations, arguments, striking out, and violent behavior Poor judgment and loss of ability to recognize danger Using the wrong word, mispronouncing words, speaking in

confusing sentences Withdrawing from social contact People with severe AD can no longer: Understand language Recognize family members Perform basic activities of daily living, such as eating, dressing, and

bathing

here is no cure for AD. The goals of treatment are:

Slow the progression of the disease (although this is difficult to do)

Manage symptoms, such as behavior problems, confusion, and sleep problems

DRUG TREATMENT

Medicines for AD include:

Donepezil (Aricept), rivastigmine (Exelon), and galantamine

, Some people believe certain vitamins and herbs may help prevent or slowdown AD

There is no strong evidence that Folate (vitamin B6), vitamin B12, and vitamin E prevent AD or slows the disease once it occurs.

By farah adulkadirMira mohamed

Nablia adamYasmeen abdelhameed